mysql search for repetition in username column

[ted_chou12]

I am very new to this, so I wish to ask a simple question about mysql.
I have built a table already, however, when signup, I wish that the php script could search for any repetitions in username before it lets the person use that username.
Thanks
Ted.

[HuggieBear]

When they submit the membership form, use a query like this:

[code]<?php
$sql = "SELECT unique_id_column FROM member_table WHERE username = '{$_POST['username']}'";
$result = mysql_query($sql);
?>[/code]

Then use the mysql_num_rows() function...

[code]<?php
if (mysql_num_rows($result) > 0){
  echo "Username taken\n";
else {
  // Insert the new user into the database
}
?>[/code]

Regards
Huggie

[ted_chou12]

Thanks HuggieBear, but I have a small question:
[code]
mysql_num_rows($result) > 1
[/code]
what I dont understand here is the ">" symbols and the number "1", could anyone explain it to me?
Thanks
Ted.

[HuggieBear]

I edited that code slightly...

mysql_num_rows() returns the number of rows found when the query's executed.  If it found more than 0 rows (> 0) then the username must exist, meaning you can't have that username.

Regards
Huggie

[ted_chou12]

thanks,
I am able to replce:
member_table
username
but I dont understand:
unique_id_column
What should I replace this with, on a tutorial they just have a * instead of words... ???
Thanks

[kamasheto]

Basically it saves query usage if you insert a name (or you called it a word?)

What unique_id_column is, is just a column name in your table, it's doesn't actually matter what column you're calling for as long as your WHERE clause is correctly taken care of. For example, if my table looks like this;

[table]
[tr][td]id[/td][td]username[/td][td]password[/td][/tr]
[tr][td]1[/td][td]kamasheto[/td][td]password[/td][/tr]
[tr][td]2[/td][td]username[/td][td]password[/td][/tr]
[/table]

And I try registering the username kamasheto with this query;

[code]SELECT id FROM members WHERE username='kamasheto';[/code]
Then I'll get this row returning;

[table]
[tr][td]id[/td][/tr]
[tr][td]1[/td][/tr]
[/table]

This when passed through mysql_num_rows(); will give me a true value of 1, which will produce an error as desired. If you decide you want to select * (means all the columns), your query;

[code]SELECT * FROM members WHERE username='kamasheto';[/code]

will return

[table]
[tr][td]id[/td][td]username[/td][td]password[/td][/tr]
[tr][td]1[/td][td]kamasheto[/td][td]password[/td][/tr]
[/table]

Which when passed through mysql_num_rows() will give the same result, 1 returned row. The only limitation to calling a specific column(s) is that in your fetching process (using mysql_fetch_array with the while loop), you'll be able to only use those columns. For example in my first query where I called for ONLY the id, I cannot check for the password using that same query, I'll have to call for a new query hence. However with my second query, I can always fetch the entire array anytime down the script.

Helpful enough?

[ted_chou12]

oh, thanks ;) I understand it completely now.